In recent years, head-up displays (HUDs) which can directly display speed information and the like on a screen (for example, a windshield of a car) are used. In an exemplary HUD, the distribution of light emitted from a light-emitting element is controlled by a lens (light flux controlling member), and then the light is projected onto a screen through a liquid crystal panel and the like. Thus a user can recognize the projected information from reflection light from the screen.
In HUDs, a surface light source device using a plurality of light-emitting elements (for example, LEDs) can be employed as the light source. However, the surface light source device using a plurality of light-emitting elements might cause luminance unevenness with a high luminance region and a low luminance region on the emission surface of the surface light source device. In view of this, some methods have been proposed to reduce such luminance unevenness (for example, PTL 1).
FIG. 1A is a sectional view illustrating a configuration of surface light source device 10 disclosed in PTL 1, FIG. 1B is a schematic plan view illustrating lens array 14 provided in surface light source device 10 disclosed in PTL 1, FIG. 1C is a graph showing a luminance distribution (relative luminance) of light emitted from lens array 14 disclosed in PTL 1, and FIG. 1D is a graph showing a luminance distribution (relative luminance) of light emitted from a lens array having no irregularity at the boundary line between adjacent two lenses.
Surface light source device 10 disclosed in PTL 1 includes a plurality of LEDs 12 disposed on substrate 11, lens array 14, and diffusion member 15. As illustrated in FIG. 1A, seven LEDs 12 are disposed in a line on surface light source device 10. In addition, as illustrated in FIG. 1B, seven lenses 13 corresponding to seven LEDs 12 are disposed in a line on lens array 14. Irregular part 17 is formed on boundary line 16 between adjacent two lenses 13 of lens array 14. In surface light source device 10 disclosed in PTL 1, the light emitted from LED 12 is converged at lenses 13, and the converged light is diffused by diffusion member 15. At this time, the luminance of the light emitted from lens array 14 is equalized by irregular part 17. Thus, in comparison with the case where no irregularity is formed (see FIG. 1D), surface light source device 10 disclosed in PTL 1 reduces the difference in luminance between the high luminance region and the low luminance region (see FIG. 1C).